Filter leaf and method of making the same

ABSTRACT

A filter leaf having a pair of spaced sheets disposed on opposite sides of a porous metallic spacer. At least one of such sheets consists of filter cloth through which a liquid flows to the spacer and thence to a peripheral or central outlet in the leaf. The spacer is desirably made from coarse woven wire cloth or expanded metal and is sprayed with a brazing material on one side thereof. The spacer and sheets are positioned together in a brazing furnace with a metallic sealing ring surrounding the spacer. Brazing material flows to the areas of contact between the sheets and the spacer, to establish a number of metallurgically bonded connections between the sheets and the areas of contact between the sheets and the spacer, to establish a number of metallurgically bonded connections between the sheets and the spacer and prevent movement of the sheets relative to the spacer.

[451 July 25,1972

[54] FILTER LEAF AND METHOD OF MAKING THE SAME [72] lnventor:

[73] Assignee:

Clark B. Burkhart, Livonia, Mich.

AMBAC Industries, Incorporated, Garden City, NY.

221 Filed: Dec. 17, 1969 21 Appl.No.: 885,833

FOREIGN PATENTS OR APPLICATIONS 73,660 9/1916 Austria ..210/486 PrimaryExaminer-John Adee Att0rneyHarness, Dickey & Pierce [5 7] ABSTRACT Afilter leaf having a pair of spaced sheets disposed on opposite sides ofa porous metallic spacer. At least one of such sheets consists of filtercloth through which a liquid flows to the spacer and thence to aperipheral or central outlet in the leaf. The spacer is desirably madefrom coarse woven wire cloth or expanded metal and is sprayed with abrazing material on one side thereof. The spacer and sheets arepositioned together in a brazing furnace with a metallic sealing ringsurrounding the spacer. Brazing material flows to the areas of contactbetween the sheets and the spacer, to establish a number ofmetallurgically bonded connections between the sheets and the areas ofcontact between the sheets and the spacer, to establish a number ofmetallurgically bonded connections between the sheets and the spacer andprevent movement of the sheets relative to the spacer.

12 Claims, 5 Drawing Figures FILTER LEAF AND METHOD OF MAKING THE SAMESUMMARY OF THE INVENTION In conventional filter leaf construction a pairof filter sheets are held on opposite sides of a spacer by means of aU-shaped binder or the like at the outer periphery of the leaf. A numberof such filter leaves are fitted to a collecting pipe within a tank.Fluid flows through the sheets from the outer sides thereof to thespacer. The spacer is porous and provides a drainage path for the flowof filtered fluid to the collecting pipe. Diatomaceous earth or otherloose filtering material may be applied to the outer surfaces of thesheets.

A serious problem exists in the maintenance of filter leaves andparticularly the periodic cleaning of the leaves. One of the mostdesirable methods of cleaning filter leaves is by back washing" them.This refers to the reverse flow of fluid from the collecting pipe to thespacer and thence outwardly through the filtering sheets. This process,however, applies a force to the filter cloth or sheets tending todisplace them away from the spacer. Because the filtering sheets havebeen secured to the spacer only at their outer periphery, the backwashing operation has had a tendency to impart a permanent outwarddistortion to the filter sheets and has caused premature destruction ofthe product.

Another method of cleaning filter leaves involves the use of a scraperblade to wipe the filter sheets. In prior constructions, however,peripheral binders have protruded outwardly of the planes of the filtersheets and have interfered with the use of wiper blades. Such anon-planar outer surface configuration of the filter leaves also impedesthe spray cleaning of the filter leaves or the removal of sludge byrotating the leaves.

The filter leaf of the present invention is intended to overcome theforegoing problems and to provide a filter leaf which is durable inconstruction, supported against outward distortion, readily cleaned,reliable in the use and susceptible of manufacture at a reasonable cost.This filter leaf construction is characterized by the use of a diffusionbonding to achieve a large number of metallurgical bonds between thespacer and the filter cloth at the contact points therebetween.

DESCRIPTION OF THE VIEWS OF THE DRAWINGS FIG. 1 is a perspective viewwith parts broken away of a filter mechanism employing filter leavesconstructed according to the present invention;

FIG. 2 is a broken sectional view of the structure illustrated in FIG. 1taken along the line 22 thereof;

FIG. 3 is a sectional view of another filter mechanism employing amodified form of filter leaf made according to the present invention;and

FIGS. 4 and 5 are sectional views of the structure illustrated in FIG. 3taken along the lines 44 and 5-5 thereof respectively.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS OF THE INVENTION FIG. 1 showsa filter tank in the form of a hollow cylinder oriented with its axes ina horizontal plane. The tank 10 has an inlet 12, a central, axiallyextending collecting pipe 14 and an outlet 16 at one end of the pipe 14.A plurality of filter leaves 18 are positioned in axially spacedrelationship along the pipe 14 and each leaf l8 registers with aseparate opening 20 in the pipe.

The construction of each filter leaf will be seen in FIG. 2. The filterleaf 18 includes a non-porous sheet 22, a sheet 24 made from fine wovenwire cloth and a spacer 26 made from coarse woven wire cloth. Sheet 22is made from sheet steel or other metal. The filter leaf I8 is of agenerally disk-shaped or circular configuration, with a central opening28 of a size permitting the filter leaf to be fitted snugly but slidablyover the pipe 14.

The space between the sheets 22 and 24 is sealed at the outer peripheryof the filter leaf by means of an annular sealing ring 30. The sealingring flatly contacts the sheets 22 and 24 on its opposite sides and isjoined to the sheets 22 and 24 by brazing material as well as by tackwelding. The spacer 26 is joined to the sheet 24 by brazing material atjoints 32 formed where the sheet 24 contacts the spacer. Similarly, thespacer 26 is brazed to the sheet 22 at joints 34 formed at each of theareas of contact between the sheet 22 and the spacer.

From the foregoing it will be seen that fluid is free to flow throughthe sheet 24 from the outer surface 38 thereof into the spaces providedbetween the individual wires of the spacer 26. From this location thefiltered fluid flows radially inwardly to the opening 20 with which theparticular filter leaf registers. Gaskets 36 are provided on oppositesides of the filter leaf to prevent leakage of unfiltered fluid directlyinto the openings 20.

It will be seen that the tank 10 can be drained through a drain outlet40. The cleaning of the individual filter leaves is aided by rotatingthe pipe 14 by means of a crank arm 41 at one end thereof. The filterleaf 18 may be used either as illustrated in the drawings or by applyinga coating of diatomaceous earth or other particulate filtering materialto the outer surface 38 of the filter sheet 24.

The geometric shape of each filter leaf 18 as seen in plan view is notcritical to the present invention. While the filter leaves 18 are ofcircular configuration as seen in plan view, they may also be squareshaped or possess a variety of other configurations. It will also beseen that the filter leaf 18 has an outlet at its center. It is withinthe contemplation of the present invention to provide a filter leafhaving an outlet at its outer periphery. Such a filter leaf isillustrated in FIGS. 3 to 5. The method of manufacturing the filter leaf18 as well as the filter leaf illustrated in FIGS. 3 to 5 will beexplained after the description of the filter leaves shown in FIGS. 3 to5.

FIG. 3 discloses a filter tank 42 having an inlet 44 and a collectingpipe 46. An outlet fitting 48 is provided at one end of the collectingpipe 46. A plurality of identical filter leaves 50 are positioned inspaced locations along the collecting pipe 46. Each of the leaves 50includes a pair of spaced woven wire cloth filter sheets 52 disposed onopposite sides of a spacer 54. The spacer 54 is made from expanded metaland is surrounded by a metallic sealing ring 56. An outlet fitting 58 issecured to the outer periphery of the filter leaf 50 and is providedwith a hollow nipple 60 received within an upstanding sleeve 62 on thecollecting pipe 46. Each sleeve 62 registers with an opening 64 in thepipe 46 while the nipple 60 is in communication with the spacer 54through a gap or interruption 66 in the ring 56. A gasket 68 aids insealing the joint between the nipple 60 and the sleeve 62.

The sheets 52 are brazed to the spacer 54 at joints 72 formed at allareas of contact between said sheets and the spacer. It will, of course,be apparent that the spacer 54 is porous in nature and provides a pathfor the flow of fluid from the space between the sheets 52 to the nipple60. Cleaning of the filter leaf 50 is aided by a spray head 74 Operableto direct jets of cleaning fluid generally tangentially along the outersurfaces of the sheets 52. The tank 42 may be drained through a drain70.

Manufacture of the filter leaves 50 is substantially the same as themanufacture of the filter leaves 18. However, the process will bedescribed with respect to the filter leaves 18. Preferably, a lightcoating of nickel brazing material (not shown) is applied to one side ofthe spacer 34. The brazing material is in a fine powdered form and issprayed by means of conventional electrostatic spraying techniques.Next, the ring 30 is tack welded to the sheet 22 in the positionillustrated in FIG. 2. The exposed surface of the ring 30 is also spraycoated with brazing material. The spacer 26 is then held on the sheet 22within the ring 30 and with the spray coated side of the spacer incontact with the sheet 22. The sheet 24 is then laid over the spacer 26and ring 30 and is tack welded to the ring 30. The tack welding of thering 30 to the sheets 22 and 24 leaves weldments (not shown) atcircumferentially spaced locations around the filter leaf. Suchweldments serve only to position the parts properly during thesubsequent brazing operation. The assembly is then positioned in abrazing furnace with the sheets 22 and 24 arranged in a horizontalattitude and held against the spacer 26 by ceramic plates (not shown). Astack of filter leaves 18 may be positioned within the furnace with aseparate ceramic plate between each filter leaf. The weight of thefilter leaves 18 and ceramic plates applies pressure to the oppositesides of each filter leaf to establish the desired contact between thesheets 22 and 24 and the spacer 26. The stack of filter leaves 18 isthen subjected to a brazing temperature for a suitable length of timeduring which the brazing material will flow by wicking to all of thejoints where the wires of the spacer 26 overlap and to the areas ofcontact 32 and 34 between the spacer 26 and the sheets 22 and 24. Extrabrazing material is also laid at the outer periphery of the ring 30 asindicated at 76 to assure a good brazed joint between the ring 30 andthe sheet 22. Of course, the sheet 24 is brazed to the ring 30.

The manufacture of the filter leaf 50 is essentially the same as thatdescribed for the filter leaf 18. It is only necessary to add extrabrazing material at the joints between the fitting 58 and the sheets 52to insure a proper seal therebetween. As in the first embodiment, onlyone side of the spacer 54 is spray coated with brazing material. In thiscase, however, to percent of the pores of the sheet 52 in contact withthe sprayed side of the spacer 54 are plugged with brazing material. Thepores of the other sheet 52 are left virtually unplugged by brazingmaterial except at the joints 72. A sufficient number of the pores ofthe screen 52 in contact with the sprayed side of the spacer remainunplugged to render the use of two porous sheets desirable for manyapplications. It is to be emphasized, however, that the magnitude ofbrazing material applied to the spacer 26 or 54 should be very slight toavoid undesirable plugging of the pores of the screen 24 or the screens52. With a little experimentation, the optimum amount of brazingmaterial can be determined. In various tested forms of the inventionillustrated in FIGS. 1 to 3, the spacer 26 was made from different sizedwoven wire cloth. In some cases the spacer had four wires to the inchwith the wires possessing a diameter of 0.063 inch. In other cases thespacer had only one wire to the inch and this wire was 0.120 inch indiameter. While spacers of this size range work satisfactorily, it isbelieved that various other sized spacers would also perform well.Likewise a variety of fine woven wire cloth materials may be used forthe sheets 24 and 52, 24 1l0 Dutch weave and 60x50 twill weave materialshaving been found to operate satisfactorily. A variety of metal alloysmight be used for the spacer and filter cloth although stainless steelwas found to be entirely suitable.

The joints 32, 34 and 72 have been described as brazed joints. Whilebrazing is the preferred technique of achieving the desired jointsbetween the spacer and the filter cloths, the invention in its broadestscope contemplates any metallurgical bond at such joints. The methodsfor achieving such a bond may be said to fall under the general headingof diffusion bonding, brazing and sinterin g being the most common formsof diffusion bonding. It should be mentioned, however, that experimentsto date indicate that brazing is lest costly than sintering and producesa superior bond.

What is claimed is:

l. A filter leaf consisting essentially of a pair of spaced parallelflat metallic sheets at least one of which comprises a fine woven wirecloth, a unitary porous metallic spacer disposed between said sheets andin engagement therewith at a large number of spaced locationsdistributed over substantially the entire areas thereof, and a sealingring surrounding said spacer in the space between said sheets andsealing the space between said sheets at the outer peripheries thereof,said at least one porous sheet being diffusion bonded to said spacer atsubstantially all of the contact locations therebetween whereby saidsheets and spacer are united into a single rigid structure in whichmovement of any portion of said sheets away from said spacer is prevented 2. The structure as set forth in claim 1 in which said at least onesheet is brazed to said spacer at substantially all of the contactlocations therebetween and is brazed to said ring.

3. The structure set forth in claim 1 in which said spacer comprises acoarse woven wire cloth and in which said contact locations between saidspacer and said at least one sheet are disposed adjacent the areas ofsaid spacer where the wires thereof overlap one another.

4. The structure set forth in claim 1 in which said sealing ring isdisposed wholly between said sheets.

5. The structure as set forth in claim 1 in which said ring and saidspacer are of the same thickness and hold said sheets apart a uniformdistance throughout the entire areas thereof.

6. The structure set forth in claim 1 in which said brazing materialalso joins said sheets to said sealing ring.

7. The structure set forth in claim 1 in which said ring is of acontinuous shape and in which the filter leaf is provided with anopening at its center for conducting fluid from the space between saidsheets.

8. The structure set forth in claim 1 in which said ring is providedwith a gap and an outlet fitting positioned on said filter leaf at saidgap to conduct fluid from the space between said sheets and through saidgap.

9. The method of manufacturing a filter leaf comprising the steps ofdistributing a brazing material over a porous metallic spacer, placingthe spacer in a brazing furnace between a pair of sheets, at least oneof said sheets comprising a fine woven wire mesh, positioning a sealingring between said sheets in a surrounding relationship to said spacer,said sealing ring being of a thickness substantially equal to thethickness of said spacer, applying a force to the opposite sides of saidsheets to hold said sheets in intimate contact with said spacer andsubjecting said spacer and sheets to a brazing temperature sufficient tocause said brazing material to flow to the points of contact of saidspacer with said sheets and form brazed joints at said points of contactwhereby said sheets, spacer and ring are united into a single rigidstructure in which movement of any portion of said mesh away from saidspacer is prevented.

10. The method set forth in claim 9 in which the brazing material isapplied to one side only of the spacer.

11. The method set forth in claim 9 in which brazing material is alsoapplied to at least one side of the sealing ring to braze at least oneof said sheets to the sealing ring.

12. The method set forth in claim 9 in which said sheets are secured tosaid sealing ring prior to the placement of the sheets, sealing ring andspacer in the furnace to maintain the proper relative positioning ofsaid parts during the brazing operation.

1. A filter leaf consisting essentially of a pair of spaced parallelflat metallic sheets at least one of which comprises a fine woven wirecloth, a unitary porous metallic spacer disposed between said sheets andin engagement therewith at a large number of spaced locationsdistributed over substantially the entire areas thereof, and a sealingring surrounding said spacer in the space between said sheets andsealing the space between said sheets at the outer peripheries thereof,said at least one porous sheet being diffusion bonded to said spacer atsubstantially all of the contact locations therebetween whereby saidsheets and spacer are united into a single rigid structure in whichmovement of any portion of said sheets away from said spacer isprevented.
 2. The structure as set forth in claim 1 in which said atleast one sheet is brazed to said spacer at substantially all of thecontact locations therebetween and is brazed to said ring.
 3. Thestructure set forth in claim 1 in which said spacer comprises a coarsewoven wire cloth and in which said contact locations between said spacerand said at least one sheet are disposed adjacent the areas of saidspacer where the wires thereof overlap one another.
 4. The structure setforth in claim 1 in which said sealing ring is disposed wholly betweensaid sheets.
 5. The structure as set forth in claim 1 in which said ringand said spacer are of the same thickness and hold said sheets apart auniform distance throughout the entire areas thereof.
 6. The structureset forth in claim 1 in which said brazing material also joins saidsheets to said sealing ring.
 7. The structure set forth in claim 1 inwhich said ring is of a continuous shape and in which the filter leaf isprovided with an opening at its center for conducting fluid from thespace between said sheets.
 8. The structure set forth in claim 1 inwhich said ring is provided with a gap and an outlet fitting positionedon said filter leaf at said gap to conduct fluid from the space betweensaid sheets and through said gap.
 9. The method of manufacturing afilter leaf comprising the steps of distributing a brazing material overa porous metallic spacer, placing the spacer in a brazing furnacebetween a pair of sheets, at least one of said sheets comprising a finewoven wire mesh, positioning a sealing ring between said sheets in asurrounding relationship to said spacer, said sealing ring being of athickness substantially equal to the thickness of said spacer, applyinga force to the opposite sides of said sheets to hold said sheets inintimate contact with said spacer and subjecting said spacer and sheetsto a brazing temperature sufficient to cause said brazing material toflow to the points of contact of said spacer with said sheets and formbrazed joints at said points of contact whereby said sheets, spacer andring are united into a single rigid structure in which movement of anyportion of said mesh away from said spacer is prevented.
 10. The methodset forth in claim 9 in which the brazing material is applied to oneside only of the spacer.
 11. The method set forth in claim 9 in whichbrazing material is also applied to at least one side of the sealingring to braze at least one of said sheets to the sealing ring.
 12. Themethod set forth in claim 9 in which said sheets are secured to saidsealing ring prior to the placement of the sheets, sealing ring andspacer in the furnace to maintain the proper relative positioning ofsaid parts during the brazing operation.